This invention relates to a method of colouring hair and to hair colouring products.
The cosmetic colouring of hair has been known for many years. Colourants are typically classified as being temporary or permanent. In temporary colouring, the colour can be washed from the hair relatively easily. So-called permanent colouring of hair typically involves the formation of oligomeric or polymeric compounds in and/or on the hair fibre. However, the colouring is not truly permanent in the strict sense of the word because the colourants can still be washed from the hair over longer periods of time.
Therefore, there remains a need for hair colourants which are more resistant to being washed off the hair.
It is known that hair fibres contain certain enzymes in and/or on the fibre. For example, the enzyme transglutaminase has been found to be present in hair fibres. Transglutaminase catalyses the formation of covalent bonds between specific peptide-bound glutamine resides and various primary amino groups of peptide-bound lysines or polyamines, acting as aminic donor substrates.
Transglutaminase can be utilised to attach agents to body tissues, as described in WO99/36570. In the specific systems exemplified in this document, exogenous transgutaminase is used to attach polylysine or polyglutamine to skin or hair. In the only specific example of a system for application to hair, a mousse for thickening hair is described which contains a mucopolysaccharide linked to polyglutamine.
Transglutaminase substrates have been involved in the treatment of hair loss. For example, FR-A-2740331 describes cosmetic compositions for the treatment of hair which contain one or more esters of butyric acid and, optionally, a substrate for transglutaminase.
The use of exogenous transglutaminase in a cosmetic composition for forming a protective layer on the hair, skin or nails, is described in U.S. Pat. No. 5,525,336. The ingredients of the composition cross-link with the outer layer of skin, hair or nails to form the layer.
WO00/64405 describes the use of substrates for a variety of endogenous enzymes that are present in hair fibres, for the delivery of hair benefit agents to the hair.
Transglutaminase is one of the endogenous enzymes mentioned in the document.
It is well-known that hair can be treated with bleaching agents, such as hydrogen peroxide. The bleaching agents generally act either to decolourise the hair or they act on dye precursor compounds to form coloured compounds on the hair. Hair contains the pigment melanin in granular form within the hair cortex. The darker the perceived hair colour, the higher the concentration of melanin in the hair. The objective of hair bleaching compositions is to decolourise both the naturally occurring melanin pigment and in addition any synthetic pigments applied to the hair.
The present invention is based on the finding of specific systems for colouring hair which may involve the action of endogenous transglutaminase. The systems have the advantage in that the colourant may be covalently bound to the hair fibre and, therefore, more resistant to being removed by washing. The systems have the further advantage that they can involve a milder method for the treatment of hair which requires a single bleaching step only. The invention involves the recognition that, surprisingly, pretreatment of the hair with an oxidising agent serves to enhance the binding of a dye to the hair by means of transglutaminase, even though the transglutaminase enzyme, which is known to be sensitive to oxidation, would have been expected to be inactive or to have reduced activity on hair treated with an oxidising agent.
According to a first aspect of the present invention, there is provided a method of colouring hair which comprises:
treating hair with an oxidising agent; and applying to the hair either during or after treatment with the oxidising agent a composition comprising a compound which is capable of acting as a substrate for endogenous transglutaminase in and/or on the hair and which comprises a chromophore that is capable of absorbing and/or emitting light in the visible part of the electromagnetic spectrum.
In a second aspect, the invention provides a hair colouring product in the form of a kit of parts comprising a hair oxidising agent packaged separately from a composition comprising a compound which is capable of acting as a substrate for endogenous transglutaminase in and/or on the hair and which comprises a chromophore that is capable of absorbing and/or emitting light in the visible part of the electromagnetic spectrum.